Chlamydia trachomatis infections are an enormous public health burden, with an estimated 2.8 million genital infections occurring annually in the United States. Due to its obligate intracellular nature, Chlamydia has developed numerous ways to manipulate function of its host cell, including secreting effector proteins into host cells. Evidence from our laboratory suggests C. trachomatis has an active type II secretion system (T2SS) that can translocate proteins from the periplasmic space to the exterior of the bacteria and that is required for replication within infected cells. I propose to identify the components required for the formation and function of the Chlamydia T2SS by screening a library of C. trachomatis mutants for T2S deficiency and by identifying proteins that interact with the T2S apparatus components using co-immunoprecipitation with specific antibodies followed by mass spectrometry analysis. Additionally, I will use a T2S-deficient mutant isolated in our laboratory t define the T2 secretome of C. trachomatis using label-free quantitative mass spectrometry. The identity and function of these effectors molecules in numerous other bacteria include effectors that modulating host responses to infection, toxins, and enzymes that hydrolyse macromolecules such as proteins and lipids. Overall, this proposal aims to characterize the understudied T2SS in C. trachomatis. Identifying T2S effectors will provide new insights into the role(s) of this secretion system during intracellular infection, in particular if T2S substrates function to scavenge nutrients from the host cell during infection or dampen the host immune response to infection.